Faced with physical limitations, lithography engineers have developed a series of sophisticated solutions - Resolution Enhancement Technology (RET), whose core idea is to actively "manage" the diffracted light field by optimizing the illumination method and mask pattern. Immersion lithography has become a major innovation in increasing the NA path. By filling a high refractive index liquid between the projection objective and the wafer, the ceiling of NA is effectively raised from 1.0 to 1.44. This technology greatly extends the lifecycle of 193nm ArF lithography technology. Off axis illumination (OAI) uses specially designed illumination apertures to tilt light at a certain angle, changing the spatial distribution of diffracted light and allowing higher frequency diffraction orders to enter the objective lens.

Off axis illumination changes the conventional imaging of the binary mask shown in (a) through oblique illumination, resulting in a shift in the diffraction pattern shown in (b)

Phase shift mask (PSM) introduces phase control on the basis of controlling light amplitude, utilizing the principle of interference cancellation of light waves to form steeper intensity gradients at the edges of the pattern.

Phase shift mask types: (1) binary mask, (2) phase shift mask, (3) etched quartz mask (Levinson mask), (4) halftone mask. (Top) Mask, (Red) Light Energy/Phase on Mask, (Blue) Light Energy/Phase on Wafer, (Green) Light Power on Wafer, (Bottom) Photoresist on Silicon Wafer

Optical Proximity Correction (OPC) technology compensates for optical distortion during imaging by pre applying "anti distortion" processing to the mask pattern.

A schematic diagram of OPC (Optical Proximity Correction). The blue gamma shape is the shape that chip designers want to print on the wafer, the green shape is the pattern on the mask after applying optical proximity correction, and the red outline is the actual appearance of the shape printed on the wafer (very close to the expected blue target)

Although RETs technology has greatly advanced the manufacturing of large-scale integrated circuits, they are highly dependent on physical masks. The manufacturing of mask templates is not only expensive, but also has a long production cycle, which has become a huge obstacle to research and development and small-scale production. Maskless lithography technology has emerged, abandoning physical masks and adopting real-time programmable "digital masks" to directly generate exposure patterns. Maskless lithography based on digital micromirror devices (DMD) has become one of the mainstream technological paths.

Overview of DMD Image Technology

DMD is composed of millions of micro mirrors at the micrometer level that can independently flip at high speed. By precisely controlling the deflection angle of each micro mirror through a computer, any two-dimensional light intensity distribution pattern can be constructed in real time, achieving "direct writing". This transition from "physical templates" to "digital light fields" brings revolutionary advantages: design flexibility, significant cost-effectiveness, and powerful functional scalability. DMD can not only achieve on/off binary modulation, but also achieve multi-level grayscale control through high-speed pulse width modulation, making grayscale lithography easy to achieve.

Zeyou Technology ZML Series DMD Maskless Lithography Machine

Scientific instrument manufacturers represented by Zeyou Technology have promoted this technology to a wider range of laboratories and research institutions through desktop DMD maskless lithography systems. The ZML series maskless lithography machine adopts high-power LED light source, combined with DMD technology, to achieve sub micron resolution, and integrates CCD camera and autofocus system, greatly reducing the difficulty of operation.

In practical applications, such devices have been used in cutting-edge research such as electrode preparation of two-dimensional material devices and rapid prototyping of microfluidic chips, demonstrating their potential in rapid prototyping and multifunctional integration.

For semiconductor manufacturing that pursues line width and large-scale production, traditional mask lithography represented by EUV is still an irreplaceable mainstream. However, in scientific research, education, packaging MEMS、 In fields such as biochips, the requirements for research and development efficiency, cost control, and design flexibility often exceed the single pursuit of extreme resolution.

Maskless lithography technology provides engineers and researchers with efficient, cost-effective, and powerful new tools by transforming the lithography process from a "heavy asset" mode to a "lightweight" digital process. It makes micro nano processing a platform for rapid validation and implementation of more innovative ideas.

The choice of technology is not simply a matter of superiority or inferiority, but rather the wisest balance made based on a deep understanding of physical boundaries and engineering characteristics, in response to specific application requirements. What we see between restriction and freedom is a clear thread from 'following physics' to' mastering physics'.